A bump test that passes this morning proves the detector can still alarm. It does not prove the number on the display is correct. Those are two different questions, and a crew that only ever answers the first one is walking into a confined space on a reading nobody has checked in months.
What a bump test actually checks
A bump test is a short, functional check: the detector is exposed to a known concentration of gas and confirms it responds and alarms as it should. MSA recommends doing this before each day's use, and it is fast enough that a crew can run it themselves before a shift starts. It answers one question: does the alarm still work. It does not adjust anything inside the instrument, or confirm the reading itself is accurate against a known reference.
A detector can pass a bump test and still be reading incorrectly, because a bump test was never built to catch that. It is a go/no-go check, not a measurement.
What a failed bump test means
If a bump test fails, MSA recommends a full calibration straight away, before the detector is used again. A detector that failed its daily check has told you that its reading or response can no longer be trusted, and the only way to find out why is a full calibration, not a second attempt at the same bump test.
The interval a bump test does not cover
A daily bump test and a full calibration run on different clocks, and confusing them is how equipment drifts past its due date unnoticed. MSA recommends a maximum interval of six months for devices with standard XCell sensors, a recommendation from the manufacturer whose sensor is inside the unit, and exactly the source an HSE manager or auditor would ask for if the figure were questioned.
The detector's own manual sets the actual interval for that model, worth checking rather than assuming. A fleet built up over several years, with units bought at different times, is not guaranteed to share one number, and treating "six months" as a fact for every detector in a store cupboard looks harmless until an inspector asks for paperwork on the one unit actually due two months ago.
What comes back with a calibration
A full calibration is where the confusion between "checked" and "certified" shows up. Every unit TopBorneo calibrates comes back with a dated calibration certificate, a different document from a note saying the bump test was run; what that difference is, and what a certificate should show, is covered in a separate piece on this site.
A dated certificate is the only record that answers the interval question for a specific unit. A logbook entry saying "bump tested, passed" tells you the alarm worked that day, not when the detector was last calibrated, the date that decides whether the unit is due now or in four months.
Getting a fleet back on schedule
Checking the date on each unit's last certificate against its own manual, rather than a number remembered from somewhere else, is the fastest way to find out which detectors in a store cupboard are actually current.
A fleet built up over several purchases rarely has its certificates filed in one place, so working through it detector by detector is the only way to be sure. Match each serial number to its own last certificate, rather than assuming the newest-looking unit is also the most recently calibrated, and do it before a permit is signed rather than after an inspector asks.
If any unit is due, or you are not sure when one last went through a full calibration, send the make, model and serial numbers to sales (at) topborneo.com, or use WhatsApp. TopBorneo replies with the work each item needs.
Related reading
- Portable gas detector calibration: what happens on the test bench and how the interval is set.
- Calibration or certification: what is the difference?: why a certificate alone does not prove a detector was measured.
- ALTAIR 4XR and 5X servicing: model-specific servicing for MSA's ALTAIR range.
- Calibration certificate copies: requesting a copy of a certificate already on file.
- Calibration services: what TopBorneo calibrates, services and inspects.